Homeless persons in San Francisco are at very high risk for HIV infection via intravenous drug use, and also for tuberculosis, syphilis and mental illness. The prevalences of these conditions and the relationships between them are not known. We propose a long term, continuing, seroprevalence and seroconversion study of HIV, syphilis and tuberculosis, and also of mental illness, in homeless persons in San Francisco. 1200 subjects will be studied yearly for three years beginning July 1991. We will establish the prevalence of HIV infection, the extent of coinfection with syphilis and TB, and the prevalence of mental illness. We will examine drug use and drug treatment. We will determine drug use, psychiatric, and sexual risk factors for HIV. We will obtain seroconversion rates for HIV and syphilis, new infection rates for TB, and incidence rates, for psychiatric disorders. We will examine the relationships between drug use, mental illness, and HIV and other infections. The study will represent the two largest strata of the homeless population -- shelter residents and food line users. An estimated 21 % of subjects will be women. Study is anonymous but a unique identifier will be taken so that results can be notified and seroconversion rates can be calculated. Subjects will be notified of their results. HIV seropositives will be offered followup and seropositive drug users needing treatment will be offered referral. Syphilis seropositives will be referred to the San Francisco Department of Public Health (DPH).Skin test (PPD) positives will be referred to the San Francisco TB clinic. Those needing psychiatric evaluation will be referred to the DPH Tom Waddell clinic. We will determine risk factors for failure of referral.